‘Dolphins take shallow dives to decompress’
Researchers have confirmed what many biologists have long suspected — dolphins avoid the bends by taking long, shallow decompression dives after feeding at depth.
A team, led by Michael Moore at Woods Hole Oceanographic Institute, has based its findings on tiny bubbles which it has found beneath the blubber of dolphins that beached themselves, the Proceedings of the Royal Society B reported.
The bubbles were discovered by taking ultrasound scans of the animals within minutes of stranding off Cape Cod in the US.
Many biologists believe that marine mammals do not struggle, as human divers do, with decompression sickness — “the bends” — when ascending from great depths.
In humans, breathing air at the comparatively high pressures delivered by scuba equipment causes more nitrogen to be absorbed into the blood and the body’s tissues, and this nitrogen comes back out as divers ascend.
But marine mammals such as whales, dolphins, and seals are highly adept at dealing with the pressures of the deep. They slow their hearts, collapse the tiny air-filled chambers in their lungs, and channel blood to essential organs — like the brain — to conserve oxygen, and limit the build-up of nitrogen bubbles in the blood that happens at depth.
However, Moore thinks it is “naive” to think that diving mammals do not also struggle with these laws of chemistry.
If dolphins, he explained, come up too quickly then there is evidence that they “grab another gulp of air and go back down again”, in much the same way a human diver would “re-tank and re-ascend” to try to prevent the bends.
“But there’s one place you can’t do that (if you are a dolphin) and that’s sitting on the beach,” he was quoted by the BBC as saying.
— PTI
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